Parallel Processing/Parallel Programming in C#

Question

I need to process more than one function that goes and performs results returning the same type of records. I am using c# under visual studio 2010 considering the functions i have are:

class Search{
public list<wrecords> GetrecordsofAAA(string term);
public list<wrecords> GetrecordsofBBB(string term);
public list<wrecords> GetrecordsofCCC(string term);
}

and im calling the functions this way

list<wrecords> records1 = Search.GetrecordsofAAA(heart);
list<wrecords> records2 = Search.GetrecordsofBBB(heart);
list<wrecords> records3 = Search.GetrecordsofCCC(heart);

this is series processing.

I need records1, records2 and records 3 to be filled simultaneously, if possible.

See the Task class: http://msdn.microsoft.com/en-us/library/system.threading.tasks.task.aspx — Just another metaprogrammer, Sep 02 '11 at 07:28

stakx - no longer contributing · Answer 1 · 2011-09-02T07:55:19.273

Take a look at the Task Parallel Library (TPL) which was introduced in .NET Framework 4 (ie. with Visual Studio 2010). More specifically, in terms of the TPL, your problem can be solved with task parallelism.

Now, I'm not an TPL expert myself at all, but documentation suggests that you should be able to do what you want with Parallel.Invoke:

using System.Threading.Tasks;
…

List<wrecords> records1 = null;
List<wrecords> records2 = null;
List<wrecords> records3 = null;
// ^ Initialize these to any default value to prevent a compile-time error.
//   The compiler cannot know that below delegates will actually be called,
//   so without the initialization you would soon get a "use of unassigned
//   variable" error.

Parallel.Invoke(
    () => { records1 = Search.GetrecordsofAAA(heart); },
    () => { records2 = Search.GetrecordsofBBB(heart); },
    () => { records3 = Search.GetrecordsofCCC(heart); }
);

P.S.: Once your methods execute in parallel, you need to make sure that none of them has any side effects that could result in the other methods not functioning properly. (For instance, if these methods read and modify the same static fields belonging to your Search class, that could lead to problems.)

albertjan · Accepted Answer · 2011-09-23T07:17:23.847

2

//make a list of the search functions you want to call.
var Searches = new List<string, Func<string, IEnumerable<wrecord>>> {
    a => GetrecordsofAAA(a),
    a => GetrecordsofBBB(a),
    a => GetrecordsofCCC(a),
}

//Execute them in parallel and collect the results as lists of lists of wrecord
IEnumerable<IEnumerable<wrecord>> result = 
    Searches.AsParallel().Select(a => a(heart));

edited Sep 23 '11 at 07:17

answered Sep 02 '11 at 07:30

albertjan

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Um... I can't help but think you wanted to say more here? – Paul Walls Sep 02 '11 at 07:32
I accidentally hit post to early :P – albertjan Sep 02 '11 at 07:59
I figured it was that or some rogue pet interfering. :) – Paul Walls Sep 02 '11 at 10:07

score 2 · Answer 3 · answered Sep 02 '11 at 07:51

Using Task Parallel Library you can do something like:

list<wrecords> records1;
lList<wrecords> records2;
lList<wrecords> records3;

Task task1 = Task.Factory.StartNew(() => records1 = Search.GetrecordsofAAA(heart));
Task task2 = Task.Factory.StartNew(() => records2 = Search.GetrecordsofBBB(heart));
Task task3 = Task.Factory.StartNew(() => records3 = Search.GetrecordsofCCC(heart));

Task.WaitAll(task1, task2, task3); // Wait for all three tasks to finish
// Do stuff after

Parallel.Invoke does not garuntee that the operations will be asynchronous. If you need the garuntee, than use Tasks like above.

score 1 · Answer 4 · answered Sep 02 '11 at 07:46

This is a sketch of a possible solution: Create tasks for each method you want to run, start each task and then WaitAll() to wait for every task to complete.

     // Create an array of methods to run
     Func<object, List<WRecord>>[] methods = new[]
                                               {
                                                  s => GetRecordsOfAAA((string) s),
                                                  s => GetRecordsOfBBB((string) s),
                                                  s => GetRecordsOfCCC((string) s)
                                               };

     // Create an array of tasks
     Task<List<WRecord>>[] tasks = new Task<List<WRecord>>[methods.Length];

     // Create and start each task
     for (int i = 0; i < tasks.Length; i++)
     {
        tasks[i] = Task<List<WRecord>>.Factory.StartNew(methods[i], heart);
     }

     // Wait for all tasks to complete. Results are in tasks[n].Result
     Task.WaitAll(tasks);

Actually, Parallel.Invoke proposed by @stakx I think is a utility method that does exactly this, but is a bit less verbose. — Anders Forsgren, Sep 02 '11 at 07:48

Parallel Processing/Parallel Programming in C#

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